Piezo-electric device



April 28, 1931. c SAWYER 1,803,274

PIEZO ELECTRIC DEVICE Original Filed May 6, 1927 ATTORN EYS Patented Apr. 28,- 1931- UN [TED STATES.

PATENT OFFICE mm B. OF CLEVELAND HEIGHTS, OHIO, ASSIGNOR, MESNE ASSIGN- .M.E'NTS, TO THE CLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A. CORPORA- TIQN OZB' OHIO loriginal application filed Kay 6, 1927, Serial No. {89,448. Divided and this application filed January 14-, 1980. Serial No. 420,742.

This invention is a division of my copending application Serial No. 189,443 filed May 6 1927, and relates to piezo-electric material, particularly to an improved means for l.util1z1ng the piezo-electric effect of, such material.

In piezo-electric devices for use at audio frequencies, various piezo-electric materials such as quartz and the like may be employed.

1 In general, however, quartz is not sufficiently sensitive for such work, and it has been found that Rochelle salt crystals are more satisfactory because of the greater piezoelectric efl'ect that can be obtained from the 15 same. Rochelle salt crystals usually employed'for such purposes, howerer, have had certain disadvantages such as inconstancy in the piezo-electric eflect produced, non-permanency of the crystals, etc., which disadvantages have been overcome-by the present invention.

One of the objects of this invention is to provide a p'iezo-electric element of very ru ged character.

other object is to provide a piezo-electricelement of uniform character giving uni form piezo-electric results.

Another object is to provide a piezo-elec- .tric element of relatively great sensitivity or relatively great piezo-electric effect.

A further object is to provide a piezo-electric element whereby the motion of the element due to an electrostatic field may be magnified to give a correspondingly greater mechanical efi'ect.

A further object is to provide a piezo-electric element suitably constrained whereby when it is subjected to an electrostatic field it may be given a bending motion to provide 0 a magnified mechanical motion thereof. I

Another object is to provide a piezo-electric element of Rochelle salt so shapedthat it will be responsive to all frequencies.

With the above and other objects in view 5 the present invention may be said to comprise the apparatus illustrated in the accompanying drawings to be hereinafter described and particularly set forth in the accompanying claims, together with such variations and modifications thereof as will be apparent to provision of piezo-electric elements of perone skilled in the art to which the present invention appertains.

This invention contemplates generally the manent and sensitive characteristics, these elements embodying piezo-electric material suitably constrained whereby a magnified mechanical movement of thesame may be obtained when subjected to anelectrostatic field. More specifically, however, this, invention contemplates a piezo-electric element arranged to expand and contract when subjected to a given electrostatic field while suitably constrained, whereby under the influence of the electrostatic field a bending motion may be produced to obtain a magnified mechanical motion.

In the drawings, which illustrate a suitable embodiment of the present invention,

Figure 1 is a perspective view of a Rochelle salt crystal fromwhich the piezo-electric material for my invention may be obtained;

Fig. 2 is a perspective view of a slab of piezo-electric material, such as Rochelle salt, portions thereof for the device of the present invention being indicated in broken outline;

Fig. 3 is a side elevation of a piezo-electric element which is mounted upon a suitable 81 P ig. 4 is a front elevation of a piezo-electric device contemplated by the present invention which embodies a jewel or stylus for cutting phonograph records, and which, by removing the stylus, may be utilized for actuating loud speakers.

Referrring to the accompanying drawings, in which like numerals refer to like parts throughout the several views, the material for an element of the present invention may be obtained from a Rochelle salt crystal 1 "as illustrated in Fig. 1, the crystal having a major longitudinal axis c-c, a major transverse axis bb, and minor axis M. It is to be understood, however, that various other piezo-electric materials or difierent sec-' tions of the Rochelle salt crystal may be employed in constructing the element of the present invention.

As an illustration of one manner in which the improvedelement may be constructed, a

slab 2 illustrated in Fig: 2 may be cut or otherwise obtained from the crystal 1, this slab beingcut so that its parallel side faces 1;,3 are substantially perpendicular to the minor "is Crystalline axis aa of the crystal 1. In Fig. 2, two portions 4" and 5, whlch may be used for the elements of the present inventlon, are shown in broken outline, the element 4 being of trapezoidal shape, whereas the element 5 is of substantially rectangular shape. The elements 4 and 5 are preferably so cut from the slab 2 that the longitudinal axes mm and nn are disposed at substantially 45 degrees to the major crystalline axes for reasons to be further discussed. The side faces of the elements 4 and 5 obviously are substantially parallel and are parallel to the major crystalline axes. It will be understood, of course, that the elements 4 and 5 may be cut directly from the crystal 1, or a portion thereof other than the slab 2. 1 In Fig. 3 the crystal element 6, which may be of trapezoidal or rectangular shape as just described, is secured at one end to a suitable support 7 such as lead by any adhesive material 8, the material 8 being, for example, shellac, Canada balsam, or any other .desirable material. The element 6 is arranged in an upright position and a suitable electrode 11 such as tinfoil, is secured to the face 10 of the element 6 and preferably contacts with a relatively large portion thereof. A portion 13 of metal such as aluminum, or other noncrystalline material, is secured to the opposed face 9 of the element 6 and is relatively thin but of sufficient strength to constrain the crystal element 6. This constraining portion 13, as shown in Fig. 3, is preferably of substantially the same size as the crystal 6. The constraining portion 13 forms the other electrode for the piezo-electricv device, and suitable conductors 12 and 15 are secured to the portions 11 and 13, respectively. The crystal element 6 and metal constraining portion 13 constitute what may be termed the piezo electric element. The portion 13 preferably, though not necessarily, is co-extensive with the face 9 of the element 6 and is preferably secured to the same throughout the face 9 5o by suitable adhesive material. It is also secured to the support 7 by the adhesive material 8.

If the crystal portion or element 6 is cut in the manner indicated by 5 and 4 in Fig. 2 that is, at 45 to the major longitudinal axis, and is subjected to an electrostatic field by a passing current through the electrodes 11 and 13, it will tend to longitudinally expand or contract, depending upon the direction of the field. Since, however, the motion of the element 6 is constrained by the metallic noncrystalline portion 13, the element 6 is not free to elongate or contract but actually undergoes a bending motion because of the constraining member 13, whereby the upper edge 16 of the same actually has a greater mechanical motion than if the element 6 were not constrained.

The piezo-electric device shown in Fig. 4 is identical with that shown in Fig. 3 and illustrates the manner in which it can be used for making phonograph records. The element 6 shown in this View is preferably of trapezoidal shape so that it will be responsive to all frequencies and is provided at its upper edge 16 with a clamp member 17 which is secured thereto by suitable adhesive material 18, The clamp member 17 is. ro- V vided with suitable apertures 19 exten ing through adjacent sides thereof so that the apertures extending through the clamp 17 parallel to the major transverse axis of the element can receive a phonograph record cutting jewel 20. If it is desired to use the piezo-electric device for actuating an acoustic diaphragm such as a loud speaker, the openings extending through the clamp 17 parallel with the minor axis of the element and perpendicular to'the longitudinal axis thereof-may receive the actuating rod for the acoustic diaphragm.

The crystal element 6 is so oriented, as

disclosed in connection with Figs. 2 and 3,

and the actuating rod of a loud speaker cone device (not shown), if the piezo-electric device is used in connection with the same, would vibrate in a direction perpendicular to the faces 9 and 10. of the crystal portion 6.

The trapezoidal shape of the crystal portion 6 shown in Fig. 4 is particularly advan: tageous acoustically, since such a crystal portion may be considered as made up of an infinite number of portions of unequal longitudinal dimension, therefore tending to respond to an infinite number of natural periods, whereby very desirable acoustic results are obtained. Furthermore, stresses throughout the crystal are maintained more uniform b the trapezoidal. shape.

It will thus be seen that by the present invention piezoelectric elements of uniform character may be obtained since the dimensions of portions composing these elements may be made accurately equal to corresponding dimensions of other portions comprising these elements.

It will also be seen that electrodes produced according to my invention are economical in the use of piezo-electric material since only portions of desired size need be used in the element. Morever, if desired, a

relatively large number of portions may be obtained from a single piezo-electric crystal or portion thereof.

5 It will furthermore be seen that the present invention provides a piezo-electric device suitable for use in acoustic devices, which is of advantageous character and gives a relatively large mechanical response to given electrostatic impulses.

To those skilled in the art, many modifications of and widely differing embodiments and applications of my invention will sug gest themselves without departing from the spirit and scope thereof. My disclosures and the descriptions herein are purely illustratlve and are not intended to be in any sense limitmg.

What I claim is:

n 1. A piezo-electric element comprising, in

combination, a support, a member of piezoelectric material of greater length than the cross-sectional dimensions thereof and mounted at one end on said support, said 5 member being cut from a piezo crystal so that when an electrostatic field is applied at right angles to its longitudinal axis it will expand and contract along its longitudinal axis, and non-piezo-electric means secured to one longi- 0 tudinal face of said member for constraining the movement of said member when an electrostatic field is applied.

2. A piezo-electric element comprising, in combination, a support, amember of piezo- 5 electric material mounted at one end on said support and being so cut from a piezocrystal that when an electrostatic field is applied at right angles to the longitudinal axis thereof it will expand and contract along 0 said longitudinal axis and a non-piezo-electric plate secured to one longitudinal face of said member for constraining the movement thereof when an electrostatic field is applied to thereby produce a bending movement of said member perpendicular to the longitudinal axis thereof.

3. piezo-electric element comprising, in combination, a support, a member of piezoelectric material mounted at one end on said support and being so cut from a piezocrystal that when an electrostatic field is applied at right angles to the longitudinal axis thereof it will expand and contract along sa d longitudinal axis, and a non-piezo-electnc plate secured to one longitudinal face of said member for constraining the movement thereof when an electrostatic field is applied to thereby produce a bending movement of saidmember perpendicular to the longitudinal axis thereof, the transverse side faces of said member of piezo-electric'mateme] being convergent from the supported end to the free end thereof, whereby sald portion will be responsive to substantially all frequencies.

4. A piezo-electric element comprising, in combination, a su port, a member of piezoelectric material of trapezoidal shape secured at one end to said support, said member of piezo-electric material being cut from a Rochelle salt crystal at substantially to the major longitudinal crystalline axis, so that when an electrostatic field is applied at right angles to the longitudinal axis thereof it will expand and contract along its major dimension, an electrode secured to one face of said member, and a non-piezo-electric member secured to the other face of said member for constraining the movement of said member when an electrostatic field is applied to produce a bending movement of said member, said non-piezo-electric member forming the other electrode for said element.

5. In a piezo-electric device, a member of piezo-electric material which tends to expand and contract in the direction of its longitudinal axis when subjected to an electrostatic field, an electrode secured to one face of said portion, and a non-piezo-electric member secured to the other face of said portion for distributively constraining said member throughout its length to produce a bendin motion when subjected to an electrostatic eld, said non-piezo-electric member forming the other electrode for said device.

In testimony whereof I aifix my signature.

CHARLES B. SAWYER. 

